The effect of various N, P and K supply levels and their combinations on the development, yield, root system, weed infestation and fungal resistance of soya (cv. Imola) was studied in the 15th year of a long-term mineral fertilisation experiment set up on calcareous loamy chernozem soil. The ploughed soil layer contained 3% humus, 5% CaCO3 and 20% clay, and was found to be poorly supplied with P and Zn and moderately well supplied with N and K. The experiment involved 4N×4P×4K=64 treatments in 2 replications, giving a total of 128 plots. The fertilisers were applied in the form of calcium ammonium nitrate, superphosphate and potassium chloride. The groundwater depth was 13-15 m and the area was prone to drought. The main results were as follows: 1. At the beginning of flowering the soya root system penetrated to a depth of 65-70 cm. On average, approx. 8% of the roots were found in the rapidly drying 0-5 cm layer, 49% in the 5-15 cm layer and 25% in the 15-25 cm layer, i.e. a total of 80% in the ploughed layer. The maximum root density was 1.13 cm · cm-3 soil, in the 5-10 cm layer, and the minimum 0.01 cm · cm-3 soil, in the 60-70 cm layer. 2. The root length was calculated to be 2.79 km · m-2 soil surface, while the root length required for the formation of 1 t air-dry shoots was approx. 22,000 km on the NP control soil. In the case of NP overfertilisation, the root system decreased to half or a third. 3. On uninoculated control soil no nodules were formed on the roots. The number of nodules per plant dropped from 3.2 to 2.0 on inoculated soils. A maximum seed yield of 21 · ha-1 could be achieved with treatments given 100 kg · ha-1 · év-1 N and with ammonium lactate (AL)-soluble P 2O5 and K2O supply levels of 100-150 mg · kg-1. Extreme overfertilisation with N and P led to yield losses of 20-30% in this dry year, when a total of only 265 mm rainfall was recorded during the vegetation period. K fertilisation had practically no influence on the yield. 4. In the case of excessive NP fertilisation the weed cover increased from 5 to 21%, while the soya cover dropped from 78% to 56%. In this treatment the air-dry weed shoot mass on August 15th was 4 times that on the control plots, reaching a value of 2.5 t · ha-1, chiefly due to the spread of Chenopodium and Amaranthus species. 5. The degree of infection with Macrophomina phaseolina at harvest was 100% on the withered plants growing on unfertilised soil, while this value was below 5% with maximum NPK nutrition, where some of the plants were still green. The late ripening (effect) induced by overnutrition (cause) was responsible for the resistance to Macrophomina (result), since forced physiological ripening did not occur even in a dry year. 6. Excessive NP supplies reduced the number of pods and seeds per plant to around half, while N fertilisation led to a 37% improvement in the 1000-seed mass. The total air-dry aboveground biomass at harvest was only 4.3 t · ha-1 on the control soil, declining to 3.3 t · ha-1 as the result of excessive P. The total biomass was made up on average of 44% seeds, 30% stems, 22% pods and 4% roots. In the case of NP overfertilisation the seed oil content was reduced from 23% to 19%, the soil yield from 400 kg · ha-1 to 270 kg · ha-1 and the crude protein yield from 800 kg · ha-1 to 560 kg · ha-1 compared to the control.
|Number of pages||14|
|Publication status||Published - Feb 1 2003|
ASJC Scopus subject areas
- Agronomy and Crop Science